klips/cpp/algorithms/sorting/radix/lib-counting.cpp

66 lines
2.8 KiB
C++

/*#############################################################################
## Author: Shaun Reed ##
## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
## About: An example implementation of counting sort using a custom library ##
## + In support of a radix sort implementation ##
## ##
## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
###############################################################################
*/
#include "lib-counting.hpp"
#include <algorithm>
#include <vector>
#include <cstdint>
void CountingSort(std::vector<int> &array, int placeValue)
{
std::vector<int> sortedArray(array.size(), 0);
// Find the maximum value within the array to sort
int32_t maxValue = INT32_MIN;
for (const auto &val : array) maxValue = (val > maxValue) ? val : maxValue;
// Create an array with element for all *placeValues* within range of the set
// + Not the size of the array to sort, but instead a element of
// + tempArray[digit] = 0; Considering only the digit at placeValue of array[n]
// Using this vector, we have a place to count all possible digits at placeValue
std::vector<int> tempArray(10, 0);
// Count the occurrences of each digit at this placeValue within the array
// + Store the end result as tempArray[digit] = count;
// + Where digit is found at the decimal placeValue of each value within array
for (const auto &val : array) {
// Get the digit at the decimal placeValue of arrayValue
auto index = static_cast<size_t>((val / placeValue) % tempArray.size());
// Running total of each value with the same digit at decimal placeValue
tempArray[index] = tempArray[index] + 1;
}
// Count the values less than or equal to each element of tempArray
// + Since each element stores its own count, just add the count at index i-1
for (int i = 1; i < tempArray.size(); i++) {
tempArray[i] = tempArray[i] + tempArray[i - 1];
}
for (ssize_t arrayIndex = array.size() - 1; arrayIndex >= 0; arrayIndex--) {
// Get the value to consider from the unsorted array
const int &arrayValue = array[arrayIndex];
// Get the digit at the decimal placeValue of arrayValue
// + Use this index to update count of values as we use them
const auto tempIndex =
static_cast<size_t>((arrayValue / placeValue) % tempArray.size());
// Store valueCount as a reference so we can update it
int &valueCount = tempArray[tempIndex];
// Offset valueCount by 1 to allow for zero index of sortedArray
sortedArray[valueCount - 1] = arrayValue;
valueCount = valueCount - 1;
}
array = sortedArray;
}